Method of separating uranium from its ores



Patented May 26, 1953 r METHOD OF SEPABATING URANIUM! FROM ITS ORES Alvin H. A. Boss, Richard H. Farmer, and Archie G. W. Lamont, Port Hope, Ontario, Canada No Drawing. Application March 29, 1951, Serial No. 218,256. In Canada April 1, 1950 Claims.

The present invention relates to the separation of uranium from its ores. V More specifically, this invention concerns the smelting of uranium ores to form a slag of high uranium content and of low base and precious metals content. A main feature of the invention resides in the production of a slag of the characteristics set forth above which is soluble in certain acids and from which the uranium content is easily recoverable by relatively simple and economical treatment.

A slag of high uranium content is herein understood to mean that a high proportion of the uranium in the ore is in one form or another present in the slag. The reverse is considered to be true of base and precious metals in suggesting that the slag is low in content of same.

To gain an understanding of the problems involved in the recovery of uraniumirom its ores, it is convenient to examine a process typical of those now employed in many countries. Such a prior art process may be divided into three separate series of operations, viz:

(1) At mine-ore concentration. (2) At Refinery A"- a) Grinding concentrates.

Ore-dressing operations. Roasting to calcines. (b) Leaching and other chemical operations to produce unrefined black oxide of uranium. (3) At Refinery BR.efining of black oxide of uranium to an extremely high purity level.

The main ore processed for eventual separation of the metal is usually pitchblende. However, in additionto the uranium and the radium constituents of pitchblende, this ore usually contains a large number of undesirable minerals chief of which are compounds of the base metals (copper, nickel, cobalt .-iron manganese, etc.), some precious metals, arsenides and sulphides. The feed to subsequent refinery operations is a product in whichthe pitchblende has been concentrated by various mechanical steps at the mine.

When the concentrates arrive at the first refinery, the preliminary operation usually consists grinding them and screening to therequired mesh. Subsequent stepsat this refinery are designed to eliminate as many as possible of the undesirable elements. This is done by a, number of ore dressing operations which include magnetic separation, flotation, selective sorting through use of Geiger pickers and finally roasting. Such cleaning steps remove only a portion of the minerals with the result that the discharge or calcines from the roaster contain much material which must be removed by subsequent costly chemical operations.

In such a process, the calcines are usually attacked with sulphuric acid and sodium nitrate with a view to dissolving the uranium. Because the radium content of the ore is so small that the radium would be lost by itself, barium chloride is also added to the leachers. Barium is very similar to radium in chemical properties and acts as a carrier for the radium during refining thereof. The radium, together with the lead, calcium, sulphide sulphur, silica andtraces of base metal impurities remain in the residue which is filtered from the uranium bearing liquor, and this residue is entered to radium extraction operations.

In addition to uranium, the solution contains most of the undesirable base metals which were present in the roaster discharge. To remove these components requires a large number of complex chemical operations which are costly and involve considerable losses of uranium. After the unwanted base metals have been sufficiently eliminated, a black oxide of uranium is obtained as a final product of this refinery and may be shipped to another plant, or entered into further operations for ether purification prior to production of uranium metal.

The undesirable elements removed by ore dressing and chemical operations are discarded as residues to the dumping ground or in the form of waste liquors to the drain.

An appreciation of the difliculties and cost involved in the present operations may be obtained from the fact that five to six tons of chemicals may be consumed per ton of concentrates in order to dissolve uranium from the calcines and to eliminate undesirable elements in subsequent processing. As the uranium content of concentrates decreases, the consumption of chemicals naturally increases.

It is a main object of the present invention to replace or to modify the operations indicated as being carried out at refinery A in the above process and to render the separation of uranium from its ores a less expensive and more complete operation.

The main feature of the invention by which the above results may be realized consists in the smelting of the ore concentrates with suitable fluxes and reducing agents to produce a slag containing a. high proportion of the ore uranium content, said slag being readily treated for the recovery of uranium and having a very low content of the undesirable elements and minerals which are normally found to be dimcult to separate from uranium. It has been found that uranium oxides, as compared with those of the undesirable metals usually found in uranium ores, are exceedingly difficult to reduce. It has also been found that upon smelting uranium ore in the manner described, the undesirable metals will be reduced and will enter a speiss-matte, with the unreduced uranium entering a slag which may be tapped off and entered into subsequent leaching operations for the recovery of uranium.

Such smeltin will remove most of the troublesome elements encountered in uranium ores, particularly the base and precious metals, arsenic and sulphur. The resultant slag, containing a high proportion of the uranium from the ore may be treated for recovery of uranium at a much lower cost than is possible by direct leaching of the ore concentrates. or roaster discharge. Inaddition to a decrease in the cost of extracting uranium from its ores, it has been found that processes including the smelting operations noted above will result in a much more complete recovery of the uranium content of an ore and will render possible the production of a final uranium product of fissionable purity with much less extensive chemical treatment.

As the initial stage in processing the ore conh centrates, it is proposed that these be smelted in an electric furnace with appropriate fluxes and reducing agents to eliminate a high proportion ofthe base metals to a speiss-matte, leaving the uranium in a slag. For ease in subsequent treatment, the slag should be of a type easily dissolved in acid, for example, nitric acid. A furnace charge suitable for this operation might be concentrates, lime and coke in the ratios 500:30z8, though such proportions are not critical and may be varied somewhat for an ore of any particular composition, or varied more widely for ores of different compositions. The operation is so conducted to eliminate arsenic and sulphur from the slag as completely as possible (since these ele- I merits interfere seriously in subsequent operations) and to produce a speiss-matte layer of low uranium content. The latter being low in uranium and radium, and containing cobalt, bismuth, silver, etc., is of by-product value. It is contemplated that wherever the term speissmatte appears in the specification or claims of the application it is to be taken as including "speiss where a material amount of sulphides is not present in the ore.

The type of furnace utilized for the smelting operation is not important, any standard smelting furnace being suitable in most cases. The fluxes found most suitable are those of a basic character, such as the oxides or carbonates of sodium or calcium. In view of the economy,

lime has been found particularly suitable for some operations, although the character of sodium oxide has also proved to be highly effective in such a smelting operation. Where sodium .oxide, or soda ash, is used, itis usually necessary to lime the furnace with graphite bricks.

' In the smelting operation, the reducing agent acts to reduce the base metals to their metallic state and to urge them to enter the speiss-matte. Highly satisfactory results have however been obtained on unoxidized ores even in the absence of 'a separate reducing agent since the reduction is accomplished by gangue sulphides and arsenides. Coke may be added if necessary as a reducing .4 agent though it is desirable in the case of a suitable ore to avoid the use of coke since this has a tendency to interfere with subsequent operations.

The production of the slag of high uranium. content, low base metal, arsenic and sulphur content, which slag has proved to be readily treated for the recovery of uranium, gives rise to several advantages over the prior arti'metho'ds. of treating ore concentrates. It has been found that in such speiss-slag separations in the smelter furnace, over 99 per cent of the uranium, radium and several radio-active elements concentrate in the slag together with the calcium, silica and barium; and over 95,per cent of the undesirable base metals, arsenic and sulphur, accumulate in the speiss-matte or are otherwise separated from the slag.

In prior art processes, many ore dressing steps and large tonnages of chemicals are often required to effect such separation of the undesirable ore constituents. The slag so produced floats on top of the molten furnace charge, having a specific gravity of about 3 in some cases. v In order that the slag may preserve its amorphous and non-crystalline character on cooling after discharge from the furnace, thus enhancing the solubility of the uranium contained therein, we prefer to quench the molten slag as it dis charges from the furnace by directing'upon the said moltenslag a high pressurejet of water. A further advantage to be derived from this quenching operation isin the ease with which the resultant granulated product may be handled.

Under certain fiux smelting and quenching conditions, smelting always being carried onto fuse a floating charge and hence usually at a ternperature between 1200 C. and 1400' C. to giyea fluid melt, a slag can be obtained from which the uranium may be readily leached with nitric acid. A slag produced by the smelting operation with lime and coke such as described above will have this acid soluble character, and recovery of uranium from this slag exceeding 99 per centmay be expected by appropriate methods of slag treatment with nitric acid or sulphuric acid.

It is at present believed that where a fifteen per cent U308 concentrate is-treated the overall uranium recovery for the present process and a suitable leaching process will show an increase of --between two and three per cent over the recovery economically possible using prior art methods. If a concentrate of 8% grade is treated the improvementover prior art'methods in the recovery of uranium should'be between five and six per cent. Moreover, since the speissslag separation causes most of the base and precious metals to enter the speiss-matte, and the radioactive elements to concentrate in the slagjit is felt that the speiss-matte constitutes a residue more susceptible to treatment for its by-product value than the residues obtained from prior art methods of uranium separation. It has also been found that the recovery of radium and other radioactive elements is facilitated by their separation into the slag in the manner described, said slag being of a character giving rise to the ready recovery of its constituents.

It is not known for certain at present in exactly What form the uranium is present in the slag after the smelting operation, whether chemically combined with some of the other compounds or whether present as oxides or ions soluble the molten slag. It is our opinion that the latter condition is the most probable one, but this is of little concern considering the advantages derived from the separation of the uranium into the slag.

The following example will best illustrate the effects of the smelting operation upon the concentrates to produce a speiss-slag separation such as described above.

Percentage Composition Concentrate Slag Speiss 13. 33 24. 3 O. 22 3. 15 19. 2 4. 50 S. 03 14. 5 28. 2 12. 4 2. 99 33. 6 2. 88 0. 21 8. '6 4. 48 0. 39 14. O 2. 96 0. l3 8. 3 3. 43 0. 08 11. 4 3. 97 7. l5 22. 6 0. 70 25. l 6. 73 0. 43 18. 0

Flux and reducing agent: 15% limestone, 2% coke. Furnace temperature: 1300 O.

smelting time: 1% hours.

Recovery of uranium: 99.5% in the slag.

From the foregoing, it will be appreciated that the present invention represents an advance in the art of the separation of uranium from its ores. In treating ore concentrates in the manner described, that is by smelting to produce a slag containing a high proportion of the ore uranium content, from which slag the uranium is readily recoverable, there is obtained a more satisfactory and economical method for the more complicated refinery operations presently employed. The smelting operation of this invention has been found to reduce considerably the cost of uranium extraction and has also been used to simplify such processes.

We claim:

1. A method for the production from uranium ore concentrates of a slag soluble in acid and carrying a high proportion of the uranium, consisting in the fusion with said concentrates of lime and a reducing agent.

2. A method for the production from uranium ore concentrates of a slag soluble in acid and of high uranium content, consisting in the fusion with said ore of lime and coke in proportions approximating eight parts of coke and thirty parts of lime to five hundred parts of said concentrates.

3. A method for the production from uranium ore concentrates having base and precious metals constituents of an acid-soluble slag high in uranium content and low in base and precious metals content, consisting in smelting together with said concentrates a basic flux and a reducing agent, whereby the base and precious metals are largely reduced and form a speiss-matte, and the unreduced uranium compounds enter said slag and separating said slag from the speissmatte.

4. In the separation of uranium from its ore concentrates, the preliminary step of smelting a reducing agent whereby any base or precious metal content in the ore is largely reduced to form a speiss-matte and a slag is produced containing a high proportion of the ore uranium content and separating said slag from the speissmatte while said slag is molten.

5. A process for the separation of uranium from its ore concentrates consisting in the smelting together with said concentrates of a basic flux and a reducing agent to form a slag containing a high proportion of the ore uranium content, separating said slag and treating said slag for recovery of uranium.

6. A process for the separation of uranium from ores containing naturally occurring reduc-' ing agents consisting in the smelting of such ore with a basic flux to form a slag containing a high proportion of the uranium content of the ore and separating said slag.

'7. A uranium slag concentrate produced by smelting a uranium bearing ore with a basic flux and a reducing agent and containing in excess of 99% of the uranium and radio-active element content of the ore and less than 5% of the base metal, arsenic and sulphur content of the ore, said slag concentrate being further characterized by its solubility in both nitric and sulphuric acid.

8. A uranium slag concentrate produced by smelting a uranium bearing ore with lime and coke and containing in excess of 99% of the uranium and radio-active element content of the ore and less than 5% of the base metal, arsenic and sulphur content of the ore, the constituents of said slag concentrate being confined to those normally present in the uranium bearing ores, in the coke and in the lime, said slag concentrate being further characterized by its solubility in both nitric and sulphuric acid.

9. A uranium slag concentrate as in claim 8 in which the lime content of the slag comprises approximately 19%.

10. A process for the treatment of uranium ores concentrates containing substantial proportions of base and precious metals, arsenic and sulphur comprising the steps of fusing said concentrates with a basic fiux and a reducing agent, whereby there is formed a speiss-matte containing a high proportion of the base and precious metals, arsenic and sulphur, and a slag containing a high proportion of the ore uranium content and separating said slag from said speiss-matte.

A. H. A. ROSS. R. H. FARMER. A. G. W. LAMONT.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Perret June 4, 1912 OTHER REFERENCES Number said concentrates together with a basic flux and 55 library, 

1. A METHOD FOR THE PRODUCTION FROM URANIUM ORE CONCENTRATES OF A SLAG SOLUBLE IN ACID AND CARRYING A HIGH PROPORTION OF THE URANIUM, CONSISTING IN THE FUSION WITH SAID CONCENTRATES OF LIME AND A REDUCING AGENT. 